Formation of small metallic precipitates of niobium in α-Al2O3 implanted with niobium ions

Niobium implantations were performed in α-Al2O3 single crystals to study the chemical interactions between the implanted species and the oxide and to study the microstructural evolution of the implanted layer. The investigation focused on both as-implanted and the oxide and to study the microstructural evolution of the implanted layer. The investigation focused on both as-implanted specimens and specimens that underwent post-implantation anneals in a reducing atmosphere. Ion implantations were performed at 300 K with 150 keV particle energies and fluences ranging from 1016 to 2 × 1017 ions cm-2. Rutherford backscattering spectroscopy (RBS) and X-ray photoemission spectroscopy (XPS) allowed the characterization of the implanted profiles and determination of the chemical state of the implanted ions. X-ray diffraction at glancing incidence and RBS analysis in a channeling geometry were performed to follow the microstructural evolution of the implanted layer. The oxidation state of niobium and the microstructure of the implanted layer were dependent on the atomic concentration of niobium in α-Al2O3. An amorphous phase was observed after a threshold fluence of 5 × 1016 ions cm-2. The amorphous phase contained small metallic precipitates of niobium with a mean diameter of 1 nm. The physical properties of such niobium clusters embedded in an amorphous oxide layer were studied in detail. Electrical conductivity measurements showed that a hopping process between the metallic precipitates was the likely mechanism operating for this system.